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ABXTEST(1)                    MPEG Audio Decoder                    ABXTEST(1)


NAME

       abxtest - double-blind ABX comparison testing script


SYNOPSIS

       abxtest [-n min] [-m max] [-g goal] A-cmd B-cmd


DESCRIPTION

       abxtest is a tool for conducting listening (or other subjective) tests
       to determine whether a listener can discern a difference between two
       subjects under test, denoted A and B.

       The listener conducts several trials in which an unknown subject, X, is
       randomly chosen to be either A or B.  The probability that X is A or B
       is the same. The listener must decide whether X sounds the same as A or
       the same as B.  The listener may repeat A, B, and X as many times as
       necessary before reaching a verdict.

       In order to prove the hypothesis that a difference can be discerned
       between A and B, the listener must disprove the null hypothesis that A
       sounds the same as B.  This is accomplished by correctly identifying X
       often enough that randomly guessing correctly the same number of times
       would be statistically improbable.

       The A and B subjects for abxtest are actually arbitrary shell commands.
       The normal mode of use would be to give commands which play two
       slightly different sounds. The standard output and standard error from
       each command are suppressed so as not to reveal the identity of X.  The
       listener may interrupt an executing command (usually by pressing ^C)
       without terminating the test.


OPTIONS

       -n min Set the minimum number of trials. Trials will continue after
              this number if the statistical probability goal has not yet been
              met. The default is 10.

       -m max Set the maximum number of trials. Trials will end after this
              number even if the statistical probability goal has not been
              met. The default is 20.

       -g goal
              Set the minimum statistical probability goal. This is the
              probability that the number of correct identifications is the
              same as random guesses. In order to disprove the null
              hypothesis, the result of the test must be a probability less
              than or equal to this goal. The default is 0.05.


FILES

       /dev/random
              By default this file is read to generate a random sequence of X.


ENVIRONMENT

       RANDOM_FILE
              If set, the file named by this variable will be read instead of
              /dev/random to generate a sequence of X.


NOTES

       abxtest uses the binomial distribution to accurately calculate the
       probability that the result is the same as random guesses.


AUTHOR

       Robert Leslie <rob@mars.org>

MAD                            16 November 2000                     ABXTEST(1)

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